Method of testing materials for surface defects



Patented Sept. 26, 1944 METHOD OF TESTING MATERIALS FOR SURFACE DEFECTS Gustav A. Jebens, Ralph H. Snell, Robert L. Heath, George A. Fisher, Jr., Donald R. Scott, and Garrett H. Mouw, Jr., Indianapolis, Ind., assignors to General Motors Corporation, De-

troit, Mich., a corporation of Delaware No Drawing. Application May 28, 1943, Serial No. 488,892

3 Claims.

It has become common practice to inspect parts, particularly metal parts, for cracks and other surface defects by immersing them in liquid capable of fluorescing when exposed to light of particular wave lengthsusually ultra-violet tion into the cracks.

are adversely affected by water.

der has proven to be diflicult.

retaining oil in the cracks.

lightremoving the excess liquid, and examining 5 ing is required as none of the materials used adthe part under such light whereupon the liquid versely affects the part being tested. in. the cracks fluoresces and reveals the defect. The improved method is subject to considerable To secure the best results the liquid in which the modification with respect to temperatures empart is immersed is heated to facilitate penetraployed and other details. Thus, the liquids, par- The part is also usually ticularly the solvent, may be applied by spraying heated at the time of examination to cause liquid instead of dippi if e t e nown deto tend to exude from the cracks and give a betgreasers may be used in place of the one specifiter indication. To further improve the indicacally mentioned. tion it has been common to dust the part with We claim: powder prior to inspection, some of the powder T e method of c e g a P for Surface adhering to the liquid exuding from the cracks defects which compris s immersing the P t in 9- and so increasing the size of the indication. hot fluorescent oil so that the defects are filled It is common to employ as the fluorescent therewith, removing the excess oil including the liquid, water soluble oils and to use water to restep of exposing the part to degreasing agent in move the excess oil. This may prove undesirable hot vapor form which serves the purpose (1) of particularly in the case of magnesium parts which removing excessive fluorescent material from the surface to better define the defects and (2) heat- While the use of powder improves the definition ing the part which increases the definition of the of the defects it is essential that all of it be re- 5 defects on subsequent examination under radiamoved after the test so that it will not cause tion capable of causing the oil in the defects to abrasion. Cleaning the parts to remove the powfluoresce.

2. The method of checking a part for surface We have found it is possible to secure better defects which comprises treating the part with a definition without employing deleterious mate- 3o fluorescent oil so that the cracks and other surrials in the testing. face defects are filled therewith, removing the According to our preferred method the part is excess oil by means of a suitable solvent, degreassubmerged for approximately twenty minutes in ing the part in degreasing vapor to remove the engine lubricating oil possessing the property of solvent and any remaining excess oil, and therefluorescence, maintained at atemperature of apafter examining the part while exposed to radiaproximately 325 F. The parts are then removed tion capable of causing the oil in the defects to and allowed to cool and drain for a few minutes. fluoresce. Thereafter they are washed or rinsed in a suitable 3. The method of checking a part for surface petroleum solvent consisting preferably of a redefects which comprises treating the part with fined distillation product of crude petroleum. 40 hot fluorescent lubricating oil to fill the defects The parts should not remain in the solvent for therewith, treating the part with an oil solvent more than approximately thirty seconds to insure to remove the excess oil, degreasing the part by the use of a hot vapor degreaser such as trichlor- While the excess solvent may then be removed ethylene vapor, to remove the solvent and any by wiping, we found that the best results are excess oil remaining, and, while still warm from obtained by degreasing the part in a vapor dethe degreasing operation, examining the part as greaser at approximately 180 F. using a suitable it is exposed to radiation capable of causing oil. vapor such as trichlorethylene." There is a two in the defects to fluoresce. fold purpose in using a vapor type degreaser (1) the removal of oil remaining on the surface and GUSTAV A. JEBENS. (2) as a source of heat for the casting which will RALPH H. SNELL. eliminate a separate operation and facilitate ROBERT L. HEATH. subsequent location of defect. Degreasing should GEORGE A. FISHER, JR. continue for no more than three minutes, other- DONALD R. SCOTT. wise too much of the oil is removed from the casting defects.

The degreasing provides a very clean surface free from any trace of fluorescent material and affords a good background contrasting with the fluorescence of the oil in the cracks.

By. employing this method no subsequent clean- GARRE'I'I H. MOUW. JR. 

